The U.S. case count in the North American E.coli outbreak linked to California-grown romaine lettuce has now risen to 52 people across 15 states, including 15 hospitalizations.
In addition, 27 ill people have been identified in Canada related to the same outbreak, according to the country's Public Health Agency.
No deaths have been reported from either country.
The U.S. Centers for Disease Control (CDC) is advising that consumers not eat any romaine lettuce from the Central Coastal growing regions of northern and central California.
The countries that are included in the investigation are Monterey, San Benito, San Luis Obispo, Santa Barbara, Santa Cruz and Ventura.
The Food and Drug Administration said in a Dec. 6 update that traceback information from four restaurants in three different states so far has implicated 10 different distributors, 12 different growers, and 11 different farms as potential sources of the contaminated lettuce.
"The information indicates that the outbreak cannot be explained by a single farm, grower, harvester, or distributor," it said.
Markets including Japan and Hong Kong have halted the entry of U.S.-grown lettuce as a precaution.